In recent years, a vertical power MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) has been developed in which a drain electrode is connected to the lower surface of a silicon substrate, a source electrode is connected to the upper surface of the silicon substrate, and a gate electrode is buried inside a trench gate formed in the silicon substrate. In such a vertical power MOSFET, it is necessary for the breakdown voltage between the drain and the source to be guaranteed not only in the cell region where the current flows between the drain and the source but also in the terminal region around the cell region. Therefore, when designing the vertical power MOSFET, it is necessary to design the terminal region to realize a prescribed breakdown voltage. Generally, guard ring structures, RESURF structures, field plate structures, and the like are known as structures of the terminal region. However, even when using these structures, there are cases where the necessary terminal breakdown voltage cannot be realized.